I am imagining that 777 has no fire detection/suppression in the E&E bay.

Somewhat wild guess (among many even wilder guesses) would suggest a slow undetected melting of various electrical components which sequentially disabled ACARS/Tpndr/ Comms / CrewO2/Control of pressurisation . . . is it possible that the depressurisation could have deprived the fire/smouldering of oxygen sufficiently to extinguish/halt the electrical carnage leaving the AP/FBW to continue serenely in Marie Celeste fashion till fuel exhaustion ?